Landforms of British Columbia 1976 - Department of Geography

“ Flat-bottomed valleys up to 3 miles wide separate the uplands. The major
valleys, which range in elevation from a few feet to 75 feet above sea-level, are as
follows: the present valley of the Fraser River; the valley occupied by the Pitt
River from Pitt Lake to the Fraser River; the valley occupied by the Alouette River
from north of Haney to the Pitt River valley; Burnaby Lake-Still Creek valley;
upper Nicomekl River-Salmon River valley; lower Nicomekl River-Serpentine
River valley; and the lower part of Campbell Creek valley. All the valleys, with
the exception of the Burnaby Lake-Still Creek valley and the present valley of the
Fraser River, are former embayments of the sea and were not cut by the streams
now occupying them.”
The Fraser Lowland includes the delta area of the Fraser River. It has been
the site of sedimentary deposition since the late Cretaceous. Deep drilling has shown
that the granitic basement is overlain by as much as 15,000 feet of late Cretaceous,
Tertiary, and Quaternary sedimentary rocks. These rocks lie unconformably above
the Coast Intrusions, and the surface of unconformity is a late Cretaceous to middle
Eocene erosion surface. Along the north side of the lowland, parts of this surface
are visible in the present topography as a long 15-degree slope. During part of the
Tertiary the old surface was saved from destruction by its sedimentary cover, but it
was exhumed and made visible by the eventual stripping by erosion of most of the
sedimentary rocks.
The area has had a very complex Pleistocene and Recent history involving
marine and non-marine, glacial and non-glacial deposition. During several glacial
advances, ice accumulated to depths of as much as 7,500 feet, and during each major
glaciation the land was depressed relative to the sea. The submergence of the land
surface based on the occurrence of marine fossils amounted to 575 feet and is interpreted
to have been as much as 1,000 feet* during the Vashon glaciation.
Recent deposits, still in the process of formation, consist of deltaic, charnel, and
flood-plain deposits of the Fraser River as it builds its delta seaward at the rate of
about 28 feett a year.
[References: Johnston, W. A., “ Geology of Fraser River Delta Map-area,”
GeoZ. Surv., Canada, Mem. 135, 1923; Armstrong, J. E,, “ Surficial Geology of
Vancouver Area,” Geol. Surv., Cunudu, Paper 55-40; Armstrong, J. E., “ Surficial
Geology of New Westminster Map-area,” Geol. Surv., Canada, Paper 57-5;
Mathews, W. H., and Shepard, F. P., “ Sedimentation of Fraser River Delta,” &z.
Ass. Pet. Geol., Vol. 46, No. 8, 1962, pp. 1416-1443.1
[Photograph: B.C. 495: 100.1
Nanaimo Lowland
The Nanaimo Lowland (see Plate VIIB) is a strip of low-lying country, below
2,000 feet elevation, which extends southeastward for 175 miles along the east coast
of Vancouver Island from Sayward on Johnstone Strait to Jordan River west of
Victoria. Denman, Hornby, Gabriola, Galiano, Pender, and Saturna Islands are
included in the lowland, which reaches its maximum width of 20 miles between
Galiano Island and Shawnigan Lake. The lowland lies on the western side of the
Georgia Depression and is largely underlain by sedimentary rocks of the Nanaimo
Group of Upper Cretaceous age. It is flanked on its western side above the 2,000-
foot contour line by the Vancouver Island Ranges, along a boundary which for at
least 70 miles roughly coincides with a major fault zone.$
* Armstrong, J. E., and Brown, W. L., Geol. Sm., An., BulI. Vol. 65, 1954, p. 362.
t This is the calculated rate of advance at a depth of 3C@ feet.
$ Buckham, A. F., Gal. Sun., Canada, Paper 41-22.
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